It has long been recognized that in any jaw chuck arrangement operating at other than relatively low rotative speeds, the centrifugal force developed on the jaws as rotative speeds increase may cause an appreciable change in the force by which the jaws engage the workpiece. This is particularly critical in chucks wherein the jaws are arranged for outside gripping, since centrifugal force tends to minimize the force by which the chuck grips the workpiece. This becomes particularly critical when the chuck is rotated at relatively high rotational speeds since the centrifugal force can reduce the gripping force to such an extent that, if the workpiece is subjected to substantial cutting pressure, the workpiece may slip within the chuck. Because of this, many conventional chucks often require that the operating speed be held below what would otherwise be possible, and in particular substantially below the higher operational speeds which are desired for maximum efficiency.
This problem has long been known and several types of counterbalanced chucks have been developed in an attempt to overcome the effects of centrifugal force. These known chucks have normally employed separate movable weights interconnected to the movable jaws by complex levers or other movable mechanisms. Needless to say, such balanced chucks have been undesirably complex both structurally and operationally, have normally required that the parts be manufactured with close dimensional tolerances, and have also normally required precisely constructed means for evenly applying a counterbalancing force onto each jaw. In addition, these counterbalanced chucks have normally been truly effective for only a narrow range of speeds, and tend at other speeds to distort the workpiece and/or the chuck structure to an undesirable extent.
Another disadvantage experienced with most known jaw chucks is the limited efficiency of these structures. Particularly, many known jaw chucks utilize a cam or wedge structure which coacts between the radially movable jaw carriers and the axially movable actuator for permitting force and motion transfer therebetween. This cam structure, which normally involves an angle which permits a self-locking of the jaw carrier, limits the efficiency of the force transfer from the actuator to the jaw carrier. It has been observed that most jaw chucks of this type have a maximum force transfer efficiency of approximately 50%, that is, the holding force developed by the jaw is approximately 50% of the axially directed actuating force imposed on the actuating wedge or cam. While attempts have been made to improve this efficiency, since any increase in this efficiency permits the chuck to have increased holding power, or in the alternative would permit a reduction in chuck size, nevertheless prior attempts have been unable to successfully appreciably increase this efficiency.
A further problem experienced with jaw chucks employing radial jaws activated by axially movable wedges, is the friction and wear experienced by the moving chuck parts, particularly the jaw carriers. The cooperation between the actuating wedge and the jaw carriers in the known structures result in the force being applied to the jaw carrier in such a manner as to result in imposition of substantial twisting or turning moments. These moments result in nonuniform pressure which accelerates the problem of wear or, in the alternative, tend to cause binding of the jaw carriers within their respective guiding slots.
Accordingly, it is an object of the present invention to provide an improved jaw chuck which is able to effectively overcome the problem created by centrifugal force when the chuck rotates at high rotative speeds, whereby the chuck thus overcomes the above-mentioned disadvantages. More specifically, it is an object of the present invention to provide:
1. A jaw chuck, as aforesaid, which includes a housing structure which structurally reacts with the jaw assemblies for resisting the centrifugal forces imposed on the jaw carriers when the chuck is rotated at high rotational speeds, thereby maintaining a substantially constant gripping force between the jaws and the workpiece.
2. A jaw chuck, as aforesaid, wherein the housing structure includes an inner sleevelike body on which the jaw carriers are radialy slidably supported, and an outer sleevelike body which surrounds and closely confines the inner body, which outer body slidably engages the wedgelike actuators which coact with the jaw carriers for preventing the centrifugal force imposed on the jaw carriers from causing any substantial reduction in the gripping force.
3. A jaw chuck, as aforesaid, wherein the jaw carriers are actuated by wedges which are axially slidably supported on and between the inner and outer bodies, which wedges and which outer body are both positioned directly radially outwardly from the jaw carriers to provide a positive backing therefor to counteract the centrifugal forces.
4. A jaw chuck, as aforesaid, wherein the jaw carriers and the cooperating actuating wedges coact in a manner which results in the force applied to the jaw carriers being substantially centrally positioned to thereby minimize the tilting and twisting forces imposed on the jaw carriers, and at the same time permitting a substantial increase in the percentage of force transmitted from the actuating wedge to the jaw carrier so as to result in a substantial increase in the gripping or holding power of the chuck.
5. A jaw chuck, as aforesaid, wherein the jaw carrier is of a substantially U-shaped configuration and has a central slot which extends radially therethrough and projects axially through the rearward end thereof, which central slot slidably accommodates therein the forward end of the actuating wedge to permit the force transfer between the jaw carrier and the wedge to occur within the central portion of the jaw carrier.
6. A jaw chuck, as aforesaid, wherein the jaw carrier has a centrally positioned wedge plate extending transversely across the central slot in an inclined relationship, which wedge plate coacts with a wedging slot formed in the wedge for permitting force transfer from the actuator wedge to the jaw carrier.
7. A jaw chuck, as aforesaid, wherein the wedge plate is removably mounted on the jaw carrier and hence can be replaced if it should experience substantial wear, without requiring replacement of the complete jaw carrier assembly.